RSA crypto attack poses threat to DRM

Side-channel code break

Security researchers have developed a new approach to breaking the RSA algorithm that creates new problems for the development of effective rights management software.

Cryptoanalysts already known the time taken to make different calculations using the same encryption key might, in theory at least, give attackers code-breaking clues in much the same way electro-magnetic leakage or power fluctuations can be used in so-called "side-channel" attacks on secure systems. The new so-called Branch Prediction Analysis (BPA) attack is a refinement on this approach that makes code breaking feasible on commodity PCs instead of expensive high-performance kit.

A carefully written spy-process, running alongside the RSA-process, is able to collect almost all the secret bits used in an RSA signing operation by monitoring the states of a CPU. The approach yields far quicker results than statistical analysis, cryptography researchers say.

"The successful extraction of almost all secret key bits by our SBPA attack against an openSSL RSA implementation proves that the often recommended blinding or so called randomization techniques to protect RSA against side-channel attacks are, in the context of SBPA attacks, totally useless," researchers Onur Aciicmez, Cetin Kaya Koc and Jean-Pierre Seifert report in their paper.

"Despite sophisticated hardware-assisted partitioning methods such as memory protection, sandboxing or even virtualisation, SBPA attacks empower an unprivileged process to successfully attack other processes running in parallel on the same processor.

The approach frustrates existing countermeasures according to crypto guru Bruce Schneier, who writes that the approach would be particularly potent if directed against Digital Rights Management (DRM) implementations. ®